Abdominal visceral fat and fasting insulin are important predictors of 24-hour GH release independent of age, gender, and other physiological factors.

Numerous physiological factors modulate GH secretion, but these variables are not independent of one another. We studied 40 younger (20-29 yr.; 21 men and 19 women) and 62 older (57-80 yr.; 35 men and 27 women) adults to determine the contributions of several demographic and physiological factors to the variability in integrated 24-h GH concentrations. Serum GH was measured every 10 min for 24 h in an enhanced sensitivity chemiluminescence assay. The predictor variables included: age group (young or old), gender, abdominal visceral fat (by computed tomography), total body fat mass and percentage body fat by dual-energy x-ray absorptiometry, serum IGF-I, fasting serum insulin, 24-h mean estradiol and testosterone, and peak oxygen uptake by graded exercise (treadmill) testing. Multiple ordinary least squares regression analysis was used to quantitatively assess the individual contribution that each predictive measure made to explain the variability among values of integrated 24-h GH concentrations while in the presence of the remaining predictors. The model explained 65% of the variance in integrated 24-h GH concentrations. Abdominal visceral fat (P < 0.002) and fasting insulin (P < 0.008) were consistently important predictors of integrated 24-h GH concentrations independent of age group, gender, and all other predictor variables. Although serum IGF-I was an important overall predictor of integrated 24-h GH concentrations (P = 0.002), this relationship was present only in the young subjects and was modulated by gender. The remaining variables failed to contribute significantly to the model. We conclude that abdominal visceral fat and fasting insulin are important predictors of integrated 24-h GH concentrations in healthy adults, independent of age and gender. Serum IGF-I is an important predictor of integrated 24-h GH concentrations in young but not older subjects. Bidirectional feedback between each of these three factors and GH secretion may account for the strong relationships observed.

The use of anthropometric and dual-energy X-ray absorptiometry (DXA) measures to estimate total abdominal and abdominal visceral fat in men and women.

OBJECTIVE: A single-slice computed tomography (CT) scan provides a criterion measure of total abdominal fat (TAF) and abdominal visceral fat (AVF), but this procedure is often prohibitive due to radiation exposure, cost, and accessibility. In the present study, the utility of anthropometric measures and estimates of trunk and abdominal fat mass by dual-energy X-ray absorptiometry (DXA) to predict CT measures of TAF and AVF (cross-sectional area, cm2) was assessed. RESEARCH METHODS AND PROCEDURES: CT measures of abdominal fat (at the level of the L4-L5 inter-vertebral space), DXA scans, and anthropometric measures were obtained in 76 Caucasian adults ages 20-80 years. RESULTS: Results demonstrated that abdominal sagittal diameter measured by anthropometry is an excellent predictor of sagittal diameter measured from a CT image (r=0.88 and 0.94; Total Error [TE]=4.1 and 3.1 cm, for men and women, respectively). In both men and women, waist circumference and abdominal sagittal diameter were the anthropometric measures most strongly associated with TAF (r=0.87 to 0.93; Standard Error of Estimate (SEE)=60.7 to 75.4 cm2) and AVF (r=0.84 to 0.93; SEE=0.7 to 30.0 cm2). The least predictive anthropometric measure of TAF or AVF was the commonly used waist-to-hip ratio (WHR). DXA estimates of trunk and abdominal fat mass were strongly associated with TAF (r=.94 to 0.97; SEE=36.9 to 50.9 cm2) and AVF (r=0.86 to 0.90; SEE=4.9 to 27.7 cm2). DISCUSSION: The present results suggest that waist circumference and/or abdominal sagittal diameter are better predictors of TAF and AVF than the more commonly used WHR. DXA trunk fat and abdominal fat appear to be slightly better predictors of TAF but not AVF compared to these anthropometric measures. Thus DXA does not offer a significant advantage over anthropometry for estimation of AVF.

Validity of methods of body composition assessment in young and older men and women.

We examined the validity of percent body fat (%Fat) estimation by two-compartment (2-Comp) hydrostatic weighing (Siri 2-Comp), 3-Comp dual-energy X-ray absorptiometry (DEXA 3-Comp), 3-Comp hydrostatic weighing corrected for the total body water (Siri 3-Comp), and anthropometric methods in young and older individuals (n = 78). A 4-Comp model of body composition served as the criterion measure of %Fat (Heymsfield 4-Comp; S. B. Heymsfield, S. Lichtman, R. N. Baumgartner, J. Wang, Y. Kamen, A. Aliprantis, and R. N. Pierson Jr., Am. J. Clin. Nutr. 52: 52-58, 1990.). Comparison of the Siri 3-Comp with the Heymsfield 4-Comp model revealed mean differences of /= r = 0.997, total error values

The influence of anatomical boundaries, age, and sex on the assessment of abdominal visceral fat.

Single-slice abdominal computed tomography (CT) scanning has been used extensively for the measurement of abdominal visceral fat (AVF). Optimal anatomical scan location and pixel density ranges have been proposed and are specifically reported to allow for the replication and standardization of AVF measurements. Standardization of the anatomical boundaries for CT measurement of AVF and the influence of age and gender on results obtained with different boundary locations have received much less attention. To determine the influence of three boundary analysis methods (AVF-1, AVF-2, and AVF-3) on the measurement of AVF by CT, 54 older (60 years to 79 years) and 37 younger (20 years to 29 years) healthy men and women were examined. The measurement boundary for AVF-1 was the internal most aspect of the abdominal and oblique muscle walls, and the posterior aspect of the vertebral body. AVF-2 used fat measurements enclosed in a boundary formed by the midpoint of the abdominal and oblique muscle walls, and the most posterior aspect of the spinous process. AVF-3 used fat measurements enclosed in a boundary formed by the external border of the abdominal and oblique muscle walls, and the external border of the erector spinae. Greater AVF measures were obtained with AVF-2 and AVF-3 compared with AVF-1 (p < 0.0001). These differences were greater in older compared with younger subjects (p < 0.0001) and greater in women compared with men (p < 0.02). The significantly greater AVF measurements obtained with AVF-2 and AVF-3 resulted from the inclusion of larger amounts of fat that are not drained by the portal circulation. This included retroperitoneal, intermuscular, and intramuscular lipid droplets, which increase with aging. On the basis of these results, we recommend the AVF-1 anatomical boundaries for the measurement of AVF in clinical investigations, particularly with older subjects. These data demonstrate the importance of precise and reproducible anatomical boundaries for the measurement of AVF, particularly in longitudinal studies.

Body composition by DEXA in older adults: accuracy and influence of scan mode.

Dual energy x-ray absorptiometry (DEXA) measures bone mineral content (BMC), bone mineral density (BMD), fat-free mass (FFM), and provides estimates of percent body fat. Changes in scan mode geometry (pencil beam vs array) may impact these measures and body composition estimates using multi-compartment models. Forty-one adults, ages 59-79 yr, were scanned in each mode and also underwent hydrostatic weighing and measurement of total body water (tritiated water dilution). The effect of scan mode on measurement of DEXA BMC, BMD, FFM, and percent body fat (DEXA %Fat) was examined. The effect of scan mode on percentage body fat determined by a 4-compartment body composition model (4 Comp %Fat) and comparison of DEXA %Fat and 4 Comp %Fat were also examined. BMC and DEXA %Fat were greater (1.3% and 3.9%, respectively, P < 0.01), and BMD and FFM were lower (1.1% and 1.9%, respectively, P < 0.01) with the array scan mode. The 4 Comp %Fat was significantly greater (0.2%) when the array scan mode measurements of total body bone mineral were used; however, these differences were physiologically inconsequential. Comparison between DEXA %Fat and 4 Comp %Fat measures revealed a total error of +/-5.0% in the older adults examined. These results indicate significant scan mode differences in total body BMC, BMD, FFM, and DEXA %Fat measurements and demonstrate the importance of using a single DEXA scan mode for clinical investigation, particularly with longitudinal studies. For all investigations with DEXA, the scan mode should be reported. Furthermore, the error associated with using DEXA alone to estimate percent fat in an older population suggests that this technique is unacceptable in a research setting.

Both oral and transdermal estrogen increase growth hormone release in postmenopausal women--a clinical research center study.

To determine if the mode of 17 beta-estradiol (E2) administration affects growth hormone (GH) concentrations, eight postmenopausal women were studied under the following conditions: (1) control (no E2), (2) oral E2 (Estrace, 1 mg every 12 h for 2 weeks) and (3) transdermal E2 (Estraderm patch, 0.1 mg, two patches changed daily for 2 weeks). Blood was collected every 5 min for 24 h and assayed for serum GH concentrations using a sensitive chemiluminescence assay. Serum E2 levels were comparable during both E2 treatment regimens when measured with a specific chemiluminescence assay. The 24-h integrated GH concentrations (IGHC, min . micrograms/L) increased in all eight subjects from (mean +/- SE) 494 +/- 102 during control to 860 +/- 111 (P < 0.05) and 832 +/- 149 (P < 0.05) during oral and transdermal E2, respectively. Both E2 treatments significantly increased GH pulse height, individual pulse area, incremental pulse amplitude, interpeak valley concentration, and interpeak valley nadir (as measured by Cluster algorithm) when compared with control. No significant differences were observed in the number of GH pulses per 24 h. Insulin-like growth factor-I (IGF-I, micrograms/L) concentrations decreased from 165 +/- 19 (control) to 109 +/- 11 (oral E2, P < 0.05) and 122 +/- 15 (transdermal E2, P < 0.05). No statistically significant differences in attributes of pulsatile GH release or IGF-I concentrations were observed between the oral and transdermal E2 treatments. We conclude that both oral and transdermal E2 treatment increase serum GH concentrations in postmenopausal women. This increase is manifested by larger GH pulses and higher basal (interpulse) GH levels, not by changes in pulse frequency. Both routes of E2 administration decrease serum IGF-I concentrations, which may attenuate IGF-I negative feedback on pituitary somatotrophs and hypothalamic somatostatin secretion, resulting in enhanced pulsatile GH release.

Contributions of exercise, body composition, and age to bone mineral density in premenopausal women.

The purpose of this cross-sectional study were to determine whether exercisers have greater bone mineral density (BMD) than nonexercisers, whether aerobic dancers have greater BMD than walkers, and to determine the contributions of energy expenditure, body composition, and dietary factors to spine and femur BMD. Measurements were obtained on 93 eumenorrheic women (walkers N = 28; aerobic dancers, N = 34; nonexercisers, N = 31) ages 25-41 yr; lumbar spine and proximal femur BMD, body composition, physical activity, and nutrient intakes. Mean height, weight, and body mass index and median age and calcium intakes were similar for the three groups. Mean (+/- SD) values of the spine, total femur, and femoral neck BMD, respectively, were: walkers (1.092 (+/- 0.098), 0.947 g.cm-2), dancers (1.070 (+/- 0.124), 0.990 (+/- 0.104), 0.908 (+/- 0.106) g.cm-2), and nonexercisers (1.020 (+/- 0.112), 0.887 (+/- 0.073), 0.792 (+/- 0.089) g.cm-2) multiple regression analyses indicated that exercise contributed to spine (P = 0.018), total femur (P =0.012), and femoral neck (P < 0.0001) BMD, whereas type of exercise (aerobic dance vs walking) did not (P > 0.05). Total femoral BMD was influenced by exercise (P = 0.012) and energy expenditure (P = 0.023), while vertebral BMD was influenced by age (P = 0.0067), body weight (P = 0.017), and exercise (P = 0.018). These findings suggest that walking and aerobic dance exercise may provide physically active premenopausal women with greater lumbar and femoral BMD than sedentary females.